Combustion engines are well-known and widely used for vehicle propulsion, power generation, for driving pumps and compressors, and for all manner of other applications. Burning virtually any combustible fuel produces certain emissions, and in many cases elimination or reduction in the relative amounts of such emissions is desirable. Smoke in the nature of unburned hydrocarbons and partially burned hydrocarbons is generally undesirable, especially in populated areas. Various oxides of nitrogen known collectively as NOx are well-known contributors to smog and the like. Significant advances in engine operating technology and construction and advanced exhaust treatment techniques have contributed to reduced emissions and cleaner air over the last several decades. For instance, so-called lean burn conditions where fuel is combusted with a stoichiometric excess of oxygen, and premixing where fuel and air are first mixed prior to being subjected to ignition conditions, have been shown to advantageously reduce certain emissions. Pilot fuels, combustion chamber shapes, particulate filters, exhaust treatment by way of selective catalytic reduction (SCR) and many other technologies exist for emissions control and efficiency optimization.
Accompanying increased interest in reduced emissions has been an expanded availability and incentives to exploit certain types of fuels less traditionally used in combustion engine, such as the various forms of biodiesel, reformed or bottled hydrogen fuel, alcohol fuels, landfill gas, and gaseous fuel derived from biomass. For at least some applications and engine designs, such fuels can burn with reduced emissions of certain types, and are also increasingly available as substitutes for more traditional fuels such as petroleum-derived hydrocarbons. Engineers are increasingly discovering, however, that engine designs, components and operating technologies may have benefits and advantages with respect to certain fuel types or classes but have more limited application or even disadvantages with respect to other fuel types or classes. U.S. Pat. No. 8,991,187 to Hughes et al. is directed to a Combustor With A Lean Pre-Nozzle Fuel Injection System. Hughes et al. appear to disclose a combustor that includes fuel nozzles, and a lean pre-nozzle fuel injection system upstream of the fuel nozzles to premix flows of fuel and air. While Hughes et al. may achieve their stated objectives, there is always room for improvement.